Recording materials sensitized to the infrared region, for example, recording materials for recording the output of near infrared beams, have been proposed in recent years. For example, there is known an image forming method using a scanner system wherein the original is scanned, and a silver halide photographic material is exposed to light on the basis of the resulting image signals to form a negative image or a positive image corresponding to the image of the original in this method, a semiconductor laser is most preferably used as the light source for recording in the scanner system. The semiconductor laser is small-sized and inexpensive, can be easily modulated, and has a working life which is longer than that of an He-Ne laser, argon laser, etc. Since the semiconductor laser emits light in the infrared region, the semiconductor laser has the further advantage that when infrared sensitive photographic materials are used, light safelight can be used and hence handleability and workability can be improved.
However, the oscillating wavelengths of the semiconductor are in the infrared region, and hence photographic materials having high light sensitivity in the infrared region are required.
Since sensitizing dyes having spectral sensitivity in the infrared region usually have a molecular band type wide absorption band, the dependence of sensitivity on the wavelengths is generally small. Accordingly, when the photographic materials are composed of a plurality of light-sensitive layers, it is difficult for individual light-sensitive layers to be selectively exposed to different laser beams. That is, color separation is deteriorated.
Accordingly, there has been a demand for a dye having sharp absorption in the infrared region.
The present inventors have studied near infrared J-band type dyes to develop dyes having sharp absorption in the infrared region. As a result, it has been found that when dicarbocyanine dyes having a specific methine chain crosslinked structure are used, J-associate in the silver halide emulsions can be formed in the infrared region, and a sharp absorption band can be obtained in the infrared region. The present-inventors have filed a patent application on the basis of this finding [see JP-A-4-146431 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")].
However, there has still been a demand for dyes having sharp absorption according to various uses.